1. Field of the Invention
The present invention relates to a process for producing a releasing film (identical with xe2x80x9crelease filmxe2x80x9d) which is of service to a pressure sensitive adhesive product and/or an adhesive product such as a pressure sensitive adhesive label and/or tape, a heat sensitive adhesive sheet and a prepreg adhesive sheet, and a releasing film which is employed as a carrier for a ceramic green sheet, synthetic leather and the like.
2. Description of the Related Arts
Most of releasing films that are employed for a pressure sensitive adhesive product and an adhesive product, and for the production of a ceramic green sheet, synthetic leather and the like are each produced at the present time by a process comprising the steps of forming a substrate film, and coating the resultant film with a silicone based releasing agent (identical with xe2x80x9csilicone based release agentxe2x80x9d) by the use of a coating machine of another production line. In order to enhance the productivity thereof, however, there has hitherto been frequently proposed a process for producing a releasing film by coating a substrate film with a silicone based releasing agent in an inline film sheeting (extrusion) step. For example, there is described in Japanese Patent Application Laid Open No. 6724/1982 (Showa 57), a process for producing a releasing film by coating a biaxially oriented polypropylene film with a heat curable silicone in an inline coating step, more specifically, there is described therein a releasing film which is produced by a process comprising extruding polypropylene with a T die, then coating the extruded polypropylene with silicone, followed by uniaxial or biaxial orientation of the same, and heat curing the silicone in orientation and annealing steps. Moreover, there is described in Japanese Patent Application Laid Open No.171916/1983 (Showa 58), a process for producing a releasing film made of biaxially oriented polypropylene film by a process comprising subjecting polypropylene film to orientation in the machine direction, coating the polypropylene film with a heat curable silicone, followed by orientation in the transverse direction, and heat setting the oriented film under restricted conditions. Further, there are described in U.S. Pat. No. 4,851,166, processes for producing biaxially oriented polypropylene film and biaxially oriented polyethylene terephthalate film, wherein the films are inline coated with a heat curable silicone as is the case with the aforesaid Japanese Patent Application Laid Open No.6724/1982 (Showa 57), but in a different manner therefrom in that such a proposal is made that the heat curable silicone is restricted in more detail, and a silicone based releasing agent should contain a reaction inhibitor and a platinum base catalyst.
The factors in common with each of the above-mentioned three proposals are that a coat of a silicone based releasing agent is applied in the production step of a biaxially oriented film, and the silicone based releasing agent is subjected to heat curing. Forever, the production process proposed in any of the three items fails to assure an energy quantity necessary for heat curing the silicone through orientation in a biaxially orientation apparatus or through heating treatment in an annealing step, whereby part of the silicone is more prone to remain unreacted. For the purpose of sufficiently heat curing the silicone, it is necessary to assure the energy by enlarging an annealing furnace or decreasing the rate of film formation, which however extremely worsening the productivity. If part of a silicone releasing agent remains unreacted in the coated layer, the releasing film fails to give the objective releasing performance (identical with xe2x80x9crelease performancexe2x80x9d), sometimes bringing about non-releasability of the releasing film to be released. Moreover in the case of preparing a pressure sensitive adhesive label and/or tape by the use of such a releasing film, the unreacted silicone migrates to a pressure sensitive adhesive layer, thus markedly deteriorating pressure sensitive adhesive properties. That is to say, it is impossible for any of the foregoing proposals to assure the releasing performance and non-migration property that are of utmost importance for a releasing film.
In such circumstances, an object of the invention is to provide a process for inline producing a biaxially oriented releasing film which process is capable of sufficiently curing a silicone based releasing agent applied to the film and therefore, is free from insufficiency in the releasing performance or migration of silicone accompanying the presence of unreacted silicone.
Other objects of the present invention will be obvious from the text of this specification hereinafter disclosed.
As a result of intensive extensive research and investigation accumulated by the present inventors in order to solve the above-mentioned problems, it has been found that a process is highly effective which comprises coating a film to be biaxially oriented with a silicone based releasing agent in the production step of the biaxially oriented film, and curing the resultant film by the combinational use of ultraviolet ray irradiation and annealing. The present invention has been accomplished on the basis of the above-mentioned findings and information.
That is to say, the present invention provides:
(1) a process for inline producing a biaxially oriented releasing film by consecutively orienting a non-oriented film in the machine and transverse directions one by one which comprises coating at least one side of a film in a state prior to biaxial orientation with an addition reaction type silicone based releasing agent, biaxially orienting said film, thereafter heat annealing the same, and subsequently performing ultraviolet ray irradiation;
(2) The process for inline producing a biaxially oriented releasing film as set forth in the preceding item (1), wherein the addition reaction type silicone based releasing agent is incorporated with a photosensitizer;
(3) The process for inline producing a biaxially oriented releasing film as set forth in the preceding item (1) or (2) wherein prior to the coating of said releasing agent, the film is subjected to surface activating treatment;
(4) The process for inline producing a biaxially oriented releasing film as set forth in any of the preceding items (1) to (3), wherein the film comprises polyethylene terephthalate or polypropylene;
(5) The process for inline producing a biaxially oriented releasing film as set forth in the preceding item (1), wherein the coating of the addition reaction type silicone based releasing agent is preceded by the orientation in the machine direction, and followed by the orientation in the transverse direction;
(6) The process for inline producing a biaxially oriented releasing film as set forth in the preceding item (1), wherein the addition reaction type silicone based releasing agent further comprises at least one member selected from the group consisting of addition reaction inhibitors, release modifiers, adhesion improvers and solvents; and
(7) The process for inline producing a biaxially oriented releasing film as set forth in the preceding item (1), wherein the ultraviolet ray irradiation is carried out with at least one non-electrode ultraviolet ray lamp.